Many perishable food products, such as diced tomatoes, are transported and stored within large cylindrical barrels or drums, e.g., 55 gallon drums. In the packaging industry, 55 gallon drums are generally classified as either tight head drums or open head drums.
Tight head drums include a hollow tubular body and circular end walls or lids. The lids are seam rolled to the top and bottom of the tubular body with a double seam rolled construction. Access to the contents of the open head drum can occur through an narrow entrance or bung which is typically in the center of one circular lid of the drum.
When an open drum is shipped to a destination, a narrow opening or bung is sometimes deemed insufficient to empty the drum of its contents. Frequently, drums must be opened to their full diameter to be emptied of their contents.
Full diameter opening of a tight head drum results in partial destruction of the drum. Typically, a cut is made through the drum cylindrical side immediately below the rolled seams which fasten the circular drum lid to the cylindrical body of the drum. Specialized cutting tools are manufactured for this purpose. With this cut made, the lid is thereafter forced off to expose the full diameter of the now open drum. Once the lid is removed, the tight head drum cannot be re-used without extensive remanufacturing.
It is known that opened tight head drums can be salvaged to form an open head drum of slightly reduced capacity. To accomplish this, a lid seat is cold rolled around the open end of the drum to form a drum seat from the cylindrical wall. The lid is thus modified so that it will engage a lid seat to close the open end of the drum. Naturally, the tight head drum is salvaged to a reduced capacity open head drum at increased cost.
So-called open head drums are known, opening to the full diameter of the transporting 55 gallon drum. Open head drums typically have a removable lid. This removable lid has a lid seat at the open end of the tubular drum body. When in place on a corresponding drum seat fashioned at the cylindrical top of the drum, and with a gasket between the drum seat and lid, the removable lid closes the drum. Unfortunately, and because of the nature of this seal, such drums are vulnerable during shipment. Specifically, where the drum is jostled during transport, both the lid and the cylindrical drum can deform. The result is that the lid momentarily separates from the drum seat. During such momentary separation, air enters the drum. This air can cause spoilage of the contents of drums carrying perishable food products such as diced tomatoes, tomato paste, fruit purees, etc.
For most commercial products shipped in open head drums, the lid is secured to the lid seat with an annular bolt ring. To open the drum and access the interior contents, the bolt ring is unlocked. Thereafter, the lid is pried off the lid seat. It is important to understand that even the protection of the annular bolt ring cannot provide sufficient protection for open head drums carrying perishable food products. A hermetic seal is required.
Open head drums have a major shortcoming. The seal between the lid and lid seat is not completely air tight, even with a bolt ring in place. When the drum is jostled during transport, flexure of both the lid and the cylindrical drum body occurs. With such dual flexure, the lid will momentarily separate from the lid seat, allowing air to enter the interior of the drum. The oxygen in the air contaminates the food products in the drum and eventually leads to product spoilage.
In regular packaging, secondary seals are used. Such secondary seals often include a membrane under a lid. This membrane acts as a seal when the lid is either removed or jostled during transport. For example, the cosmetics industry typically seals small containers, such as make-up jars, with a circular membrane that is attached to a lid seat of the jar underneath the lid. These types of secondary seals, however, would be costly to fabricate for the relatively large open head drums, and they are generally not designed to withstand the intense shaking, bouncing and jarring that open head drums are forced to undergo.